The present invention relates to a gearbox for a motor vehicle and to a method for operating the gearbox.
Gearboxes for motor vehicles are known which comprise elements which can be lubricated and/or cooled and/or hydraulically actuated by oil. A gearbox usually has an oil sump for this purpose. Gearboxes known from the prior art usually have a high oil level in the gearbox in order to be able to ensure a reliable oil supply in all driving states.
DE 1 801 917 discloses a gearbox which operates with oil sump lubrication, in particular a differential gear for the axial drive of motor vehicles. A space which is divided off by a dividing wall and is open in its upper region is arranged within the gearbox housing in such a way that at least a portion of the oil which is thrown up during operation collects therein, and in such a way that this space is connected to the main space though at least one opening.
DE 199 16 377 A1 discloses a change-speed gearbox. The change-speed gearbox contains a housing in the interior of which a rotating gearbox group and a driven shaft, which is connected to the gearbox, are mounted. A bulkhead wall is located in the gearbox, between the housing and the gearbox group.
DE 32 08 100 A1 discloses a gearbox housing with immersion lubrication, in particular for wheel hub gearboxes. In the state of rest, the gearbox housing is filled with oil up to a permissible filling level, which in the operating state is also entrained in the rotational direction by rotating gearbox parts, with the result that the entrained oil bears as an oil ring which bears on an inner lateral face of the gearbox housing and which has a thickness which is predefined by the filling volume, wherein some of the gearbox parts also have an immersion depth in the oil which is sufficient for immersion lubrication. The gearbox housing has means with which the immersion depth can be adapted to changed load states of the gearbox.
WO 2008/076061 A1 discloses a method for reducing the rotational resistance of gearwheels in a gearbox for a motor vehicle, and a gearbox. In the gearbox, the normal oil level (N1) for operating with gearwheel combinations of the gearbox during direct-gear speed operation is temporarily reduced to a level (N2) at which lower gearwheels of the gearwheel combination rotate essentially without contact with the oil in the oil sump. The oil level is increased again to the normal level (N1) after the insertion of gearwheel combinations. For this purpose, an oil collecting tank is connected to the gearbox housing. The oil collecting tank not only has an upper oil inlet in the vicinity of the housing, which inlet is subjected during operation to sprayed oil from gear wheel combinations of the gearbox of the lower gear wheels which are immersed in the oil in the oil sump, but also a lower outlet in order to feed oil which has collected in the tank back to the oil sump. The outlet can be closed off during the direct-gear speed operation in order to lower the oil level in the oil sump.
EP 1 855 030 A1 discloses a fluid equalization container for arrangement in a housing of a gearbox. The fluid equalization container comprises at least one fluid inlet for taking up fluid into the fluid equalization container, and at least one fluid outlet for discharging fluid. The fluid inlet is larger than the fluid outlet, with the result that the fluid compensation container is filled during normal operation, in order to lower the fluid level in the housing. In this context, through-flow-limiting means which are dependent on the viscosity of the fluid are arranged at the fluid inlet, said through-flow-limiting means limiting the through-flow of fluid into the fluid equalization container, with the result that the fluid level is lowered less if the viscosity of the fluid exceeds a specific limiting value.
DE 103 08 560 A1 proposes an automated gearbox for motor vehicles, in particular a gearbox in the form of a countershaft gearbox having a gearbox housing, at least one power train for setting up different transmission ratios, which power train is configured to transmit force from a gearbox input to a gearbox output, wherein force-transmitting elements are lubricated from an oil sump at the bottom of the gearbox housing, and a hydraulic arrangement which has at least one pump and a valve arrangement and is configured to activate shift elements in an automated fashion in order to change the transmission ratio of the power train. In this context, a container which serves as an oil reservoir for the hydraulic arrangement is arranged laterally next to the oil sump inside the gearbox housing.
Gear wheels which are contained in gearboxes known from the prior art usually dip at least partially into oil and as a result cause splashing losses as a function of the level of the oil.